PMD Testing

Competitive market pressures demand that service providers continuously upgrade and maintain their networks
to ensure they are able to deliver higher speed, higher quality applications and services to the customers. This requires verifying and ensuring that the network’s fiber infrastructure and equipment can meet exacting performance standards and operate reliably. Due to the increased transmission speed and implementation of DWDM systems, some important changes were made in the optical fiber characterization and system turn-up, requiring new test tools and procedures, described in different JDSU white papers.
Polarization Mode Dispersion (PMD) testing is becoming essential in the fiber characterization process, but still one of the most difficult parameter to test, due to its sensitivity to a number of environmental constraints.

Polarization Mode Dispersion definition

PMD (Polarization Mode Dispersion) is caused by the differential arrival time of the different polarization components
of the input light pulse, transmitted into an optical fiber. This light pulse can always be decomposed into pairs of orthogonal polarization modes. These polarization modes propagate at different speeds according to a slow and fast axis induced by the birefringence of the fiber.

Bi-refringence

Optical fibers are slightly bi-refringent. Bi-refringence is a property of material (e.g. optical fiber) where the effective
index of refraction varies with the polarization state of the input light.
The main causes of this bi-refringence are non-perfect concentricity and in homogeneity of the optical fiber in manufacturing design, as well as external stresses applied on the fiber cabling, such as bends, or twist.